1. Field of the Invention
The present invention relates to a valve device. More particularly, the present invention relates to a valve device with pressure alarm for a tire.
2. Description of the Related Art
A typical valve device with pressure alarm is disclosed in e.g., Taiwan Utility Model Application No. 93209317. This valve device comprises a metal housing, a transverse partitioning seat separating an interior of the metal housing into an upper compartment and a lower compartment. The transverse partitioning seat includes a central hole. The housing includes an inner shoulder in a top of the upper compartment. A valve is mounted in the lower compartment. A diaphragm is mounted on a top face of the transverse partitioning seat. A sleeve is mounted in the upper compartment and above the diaphragm, with a through-hole defined in top of the sleeve. A push rod is mounted in the sleeve, with a bottom end of the push rod abutting against the diaphragm, with a top end of the push rod extending through the through-hole of the sleeve, and with a flange formed on the push rod at a location adjacent to the bottom end of the push rod. An elastic element is mounted around the sleeve and between the flange and the top of the sleeve.
A metal contact plate is mounted on the top end of the sleeve and extends across the inner shoulder. When the tire pressure is in the normal range, the metal contact plate is moved upward by the tire pressure and thus disengaged from the inner flange. When the tire pressure is too low, the metal contact plate moves downward and comes in contact with the inner shoulder. A battery device is mounted on the top face of the metal contact plate. The battery device includes a negative pole in contact with the metal contact plate and a positive plate to which a conductive member is connected. A transmitter is mounted to the conductive member and the top of the metal housing. The transmitter includes a circuit board electrically connected to the conductive member and the metal housing. A cover is mounted around the top of the metal housing. Such a tire device sends a signal for alarm purposes only when the tire pressure is insufficient. It cannot provide an alarm effect when the tire pressure is so high that the tire may burst during driving due to friction or overload.